This Friday we have Seth's former advisor Jeremy Butterfield visiting.
He works on philosophy of physics and during the 11am group meeting will tell us about his work on symmetry and duality.
He will also give a talk at 1:30pm in room 6c-442. Here are the details.
title: Deriving time evolution in general relativity : a philosopher's
perspective. Joint work with Henrique Gomes, Cambridge.
Abstract:
Abstract: This talk will advertise three results that give, in a broadly
general-relativistic framework, sufficient conditions for time-evolution
being generated by the ADM Hamiltonian. The philosophical background is
functionalism. Roughly speaking, it is the idea that one specifies an entity
or concept by its web of relations to other entities and concepts. Recently
philosophers have debated 'spacetime functionalism': "spacetime is as
spacetime does". Thus their focus is on how the physics of matter and
radiation contributes to determining, or perhaps even determines or
explains, chrono-geometry: a Machian theme.
The results are as follows:--- (i) The recovery of
geometrodynamics, i.e. general relativity's usual ADM Hamiltonian, from
requirements on deformations of hypersurfaces in a Lorentzian spacetime;
due to Hojman, Kuchar and Teitelboim (1976: Annals of Physics); (ii) The
deduction from judicious assumptions about matter and radiation in a
4-dimensional manifold that there is an (appropriately related) Lorentzian
metric; due to Schuller, Duell, Giesel et al. (2012, 2018: Physical Review
D); (iii) The deduction of a Lorentzian metric and of general relativity's
usual ADM Hamiltonian, assuming (not a 4-manifold: but merely) that how a
3-geometry changes over time should be locally definable (Gomes and Shyam
2016: Journal of Mathematical Physics; and at 1608.08236). Thus the overall
aim of the talk is to give a philosophical background to Gomes and Shyam,
1608.08236.